Frontal upwelling in a rotating two-layer fluid     

G. J. F. Van Heijst 《地球物理与天体物理流体动力学》2013,107(1-4):139-153

Abstract

This paper describes the source-sink driven flow in a two-layer fluid confined in a rotating annulus. Light fluid is injected at the inner wall, while denser fluid is withdrawn at the outer wall. The interface between the immiscible fluids intersects the bottom and thus produces a front. The net transport from the source to the sink is carried by Ekman layers at the bottom and at the interface, and by Stewartson layers at the side walls. A detached Stewartson layer arises at the front, leading to a pronounced upwelling circulation.  相似文献   

The structure of separated flow past a circular cylinder in a rotating frame     

Michael A. Page  Peter W. Duck 《地球物理与天体物理流体动力学》2013,107(1-4):197-223

Abstract

This paper examines the detailed E ^1/4-layer structure of separated flow past a circular cylinder in a low-Rossby-number rotating fluid as the Ekman number E tends to zero. This structure is based on an initial proposal by Page (1987) but with some modifications in response to further evidence, outlined both in this paper and elsewhere, on the behaviour of E ^1/4-layer flows in this context. Numerical calculations for flow in an E ^1/4 shear layer along the separated free streamline are described and the mass flux from this layer is then used to calculate the higher-order flow within the separation bubble. The flow structure is found to have two forms, depending on the value of the O(1) parameter λ, and these are compared with results from published “Navier-Stokes” type calculations for the flow at small but finite values of E.  相似文献   

On isallobaric effect in a quasi-geostrophic topographic-drag problem     

Gregory M. Zhikharev 《地球物理与天体物理流体动力学》2013,107(1-4):101-108

Abstract

Isallobaric effect of a slowly varying quasi-geostrophic flow represented by propagating waves may give rise to a mean steady topographic drag component which turns out to be the principal one when viscous effects are negligibly small. This drag component decreases, in contrast to the quasi-geostrophic component, when statistical properties of the topography become isotropic. When the phase velocity of the incident wave is much larger (smaller) than the phase speed of Rossby waves, the isallobaric drag becomes independent (dependent) on the sign of that velocity.  相似文献   

GPS系统时间及其与其他时间的关系     

陈洪卿  王振伟 《时间频率学报》2012,35(4):201-204,234

指出不同授时规范对“GPS系统时间”定义、解释的差异,给出比较清楚和综合的“GPS系统时间”理解,这会有益于北斗系统和GPS系统组合PNT（定位、导航、授时）应用标准化。  相似文献   

基于麦夸特算法的X射线衍射物相定量分析的影响因素研究   总被引：2，自引：0，他引：2  

曾蒙秀  宋友桂 《岩矿测试》2012,31(5):798-806

X射线衍射物相定量分析方法很多,新近提出的麦夸特算法(Levenberg-Marquardt)在XRD物相定量分析中具有明显的优势,但在实际应用过程中,哪些因素会对该方法计算结果的准确度产生影响仍不清楚。为了指导实际操作过程并提高麦夸特算法在X射线衍射物相定量分析中的准确度和处理效率,本研究通过Matlab软件,将已知配比含量的刚玉、石英、方解石和钠长石与其计算值进行比较,探讨衍射峰强度、衍射峰背底、样品数量等因素对麦夸特算法应用于X射线衍射物相定量分析中计算结果的影响。结果表明:通过前三强峰法的计算结果比通过最强峰法的计算结果具有更高的准确度;由于物相晶体结构及衍射特性的差异,衍射峰背底对不同物相定量结果的影响程度各异,扣除背底后各物相计算结果的准确度整体上都有不同程度的提高;在利用麦夸特算法进行批量分析过程中,当样品数低于一定阈值时,样品数越多,计算结果的准确度提高越明显,但当计算的样品超过一定阈值时准确度不会有明显的提高。  相似文献   

三江源区高寒草地载畜量及超载状况分析(英文)     

张继平  张林波  刘伟玲  齐月  沃笑 《地理学报(英文版)》2014,(2)

The Three-River Headwaters region in China is an ecological barrier providing environmental protection and regional sustainable development for the mid-stream and downstream areas, which also plays an important role in animal husbandry in China. This study estimated the grassland yield in the Three-River Headwaters region based on MODIS NPP data, and calculated the proper livestock-carrying capacity of the grassland. We analyzed the overgrazing number and its spatial distribution characteristics through data comparison between actual and proper livestock-carrying capacity. The results showed the following:(1) total grassland yield(hay) in the Three-River Headwaters region was 10.96 million tons in 2010 with an average grassland yield of 465.70 kg/hm2(the spatial distribution presents a decreasing trend from the east and southeast to the west and northwest in turn);(2) the proper livestock-carrying capacity in the Three-River Headwaters region is 12.19 million sheep units(hereafter described as "SU"), and the average stocking capacity is 51.27 SU [the proper carrying capacity is above 100 SU/km2in the eastern counties, 60 SU/km2in the central counties(except Madoi County), and 30 SU/km2in the western counties]; and(3) total overgrazing number was 6.52 million SU in the Three-River Headwaters region in 2010, with an average overgrazing ratio of 67.88% and an average overgrazing number of 27.43 SU/km2. A higher overgrazing ratio occurred in Tongde, Xinghai, Yushu, Henan and Zêkog. There was no overgrazing in Zhiduo, Tanggula Township and Darlag, Qumerleb and Madoi. The remainder of the counties had varying degrees of overgrazing.  相似文献   

Urban Boundary-Layer Stability and Turbulent Exchange during Consecutive Episodes of Particle Air Pollution in Beijing,China          下载免费PDF全文

GUO Xiao-Feng  YANG Ting  MIAO Shi-Guang  SUN Ye-Le 《大气和海洋科学快报》2014,(1)

  相似文献   

季风涡旋影响西北太平洋台风生成初步分析   总被引：2，自引：1，他引：1       下载免费PDF全文

李肖雅  吴立广  宗慧君 《大气科学学报》2014,37(5):653-664

西北太平洋对流层低层大尺度低频环流季风涡旋与台风生成有密切的关系。利用时间滤波方法将季风涡旋和台风环流从逐日台风风场中分离出来,对两次季风涡旋活动个例分析发现,气旋初始扰动都首先出现在季风涡旋中心东部,一次季风涡旋活动可以伴随着一个或几个热带气旋的生成。通过进一步分析2000—2009年季风涡旋活动与热带气旋的生成关系发现,虽然季风涡旋的定义与环流强度和持续时间有关,但是热带气旋的生成位置大多数分布在季风涡旋的中心和东部,这可能与季风涡旋的Rossby波能量频散有关。  相似文献   

地震灾害快速自动评级方法研究     

仇新莉  刘培顺  唐瑞春 《防灾减灾学报》2021,37(1):51-60

发生地震时,需根据本次灾害的各个方面的损失程度来确定最终的应急响应级别,目前的地震等级评估办法,主要参考受伤死亡人数、房屋损伤程度、经济损失情况、烈度等,其中部分参考因素需震后较长时间调查之后才能获取,无法及时为应急响应提供参考。利用回归分析方法,对我国历史上大量地震数据进行分析,提出一种地震灾害快速自动评级的方法,综合地震震级、经济损失、受灾人数、衍生灾害等各种影响因素在震害初期快速评估出本次地震的等级,为应急响应的启动提供保障,方便救灾工作的展开。数据分析结果表明,提出的地震等级评估结果与综合灾害指数灾区分级结果基本一致,且在震害初期就能评估出地震等级,能为应急响应、地震救援工作提供参考。  相似文献   

Experimental investigation of density current patterns using dynamic fractal analysis     

Mohammad Hosseini  Mohammad Hadi Fattahi  Saeid Eslamian 《国际泥沙研究》2021,36(2):165-176

Density currents are caused by a difference in density,though low,of an entering fluid with the ambient fluid.This type of current is two-phased and found on riverbeds or in reservoirs behind dams,and is nonlinear in nature,complex,and sensitive to initial conditions.Fractal geometry is used as a powerful tool for studying complex natural phenomena.Using experimental studies and changes in inlet current conditions,the fractal and multi-fractal analyses of the interface between the density current and the ambient fluid were done.In addition,a search was made to find a possible connection between the nonlinear patterns.According to the results,with an increase in the inlet discharge and inlet density of the current the fractal dimension decreased.Further,the smaller the range of the singularity spectrum diagram was,i.e.,the more it was less than 0.34,the lower the system's tendency was to be multi-fractal,and the system sensitive to large local changes.In the interface between the density current and the ambient fluid,using the fractal dimension-based Richardson number could improve experimental data by 12.4%.Moreover,with an increase in the Richardson number,the Reynolds number of the current decreased.Further,upon considering the fractal dimension,the Reynolds number improved by 23%and a good correlation with a coefficient of determination of 0.76.  相似文献